The present invention relates to a material testing system that applies loads to a test specimen. More particularly, the present invention relates to a test specimen holder that holds the test specimen in the material testing system.
Test specimen holders are well known and are used frequently to hold a test specimen in a material testing system. Various types of test specimen holders have been advanced, which include hydraulically operated and mechanically operates wedge grips having opposed jaws. These types of test specimen holders are generally used on test specimens that can withstand the high clamping forces provided by the wedge jaws. Other test specimen holders have been advanced to hold more fragile test specimens. In one known type, screw operated actuators are positioned on opposite sides of the test specimen. Each of the screw actuators displace a jaw plate toward the other with the test specimen disposed therebetween.
The screw operated actuators also have shortcomings. For instance, misalignment of the test specimen is possible when screw actuators used in an upper grip and the screw actuators used in a lower grip are not positioned correctly with respect to the tension/compression axis of the material testing system. In addition, a reduction in clamping pressure can arise over time due to deformation of the test specimen during the test. A screw operated test specimen holder that addresses one or both of these shortcomings is therefore desired.
A first broad aspect of the present invention is a test specimen holder for holding the test specimen in a material testing machine. The test specimen holder includes a base member having an end coupleable to the material testing machine and a pair of first and second aligned, spaced apart support members. Each support member includes indicia. A pair of movable jaw assemblies are provided. A first movable jaw assembly is slidably coupled to the first support member, while the second movable jaw assembly is slidably coupled to the second support member. Each movable jaw assembly includes an indicator slidable therewith and disposed proximate the indicia of the corresponding support member.
A second broad aspect of the present invention includes a test specimen holder having a base member with an end coupleable to the material testing machine and a pair of first and second aligned, spaced apart support members. A movable jaw assembly is a adapted for each of the support members. Each jaw assembly includes a jaw plate engageable with a test specimen and an actuator adapted to selectively move the jaw plate. A first and second plurality of blocks of material are provided. Each plurality includes blocks of material of different compliance. Each block of material is adapted to be inserted between one of the actuators and the corresponding jaw plate.